This invention relates to a spinning machine having several spinning stations which are arranged on at least one side of the machine and each comprise a drafting unit. Depositing sites for cans are provided which receive the fiber material to be spun in the form of slivers. Transport devices for transporting the slivers from the cans to the drafting units are provided which each comprise one pair of delivery rollers which is connected in front of a pair of feeding rollers of the pertaining drafting unit.
It is known (British Patent Document 1 015 780) to feed the fiber material to be spun to a ring spinning machine in the form of slivers which are withdrawn from cans. The cans are deposited in several rows in front of the ring spinning machine. The slivers are withdrawn from the cans by way of rollers arranged above the cans and are guided to the drafting units of the individual spinning stations by means of transport belts. In this case, transport belts are provided which are in each case arranged in pairs, receive the slivers between one another and guide them. In the area of the drafting units, deflecting rollers of the transport belts are situated which are used as a pair of delivery rollers by means of which the slivers are in each case fed to a drafting unit. A friction roller is assigned to one of the deflecting rollers and can be brought between this deflecting roller and a bottom roller of the drafting unit so that the drive of the delivery roller pair and thus of the transport belts is diverted from the bottom feeding roller. The delivery speed of the pair of delivery rollers should therefore correspond to the feeding speed of the pair of feeding rollers of the drafting unit.
In an older German Patent Application (P 41 09 096.9), which is no prior publication, it was also suggested to let the pair of delivery rollers run at such a speed that a preliminary draft is created between the delivery roller pair and the feeding roller pair of the drafting unit so that the delivery roller pair participates in the overall draft of the sliver and thus, in a sense, is part of the drafting unit.
It is an object of the invention to develop a spinning machine of the initially mentioned type such that clear and defined conditions exist with respect to the draft during the whole operating time.
This object is achieved in that the delivery speed of the delivery roller pairs is approximately 1% to approximately 2% less than the feeding speed of the feeding roller pairs.
In this manner, it is ensured that the slivers are held in a tensioned manner between the delivery roller pairs and the feeding rollers pairs of the drafting units without any resulting draft, or at least without any draft that in practice would be important with respect to the overall draft of the drafting unit. In this case, the invention is based on the recognition that in practice certain fluctuations or irregularities in the feeding of the slivers are unavoidable. In practice, the slivers do not enter into the transport devices in a precisely straight manner but rather in a slightly wave form which is more or less pronounced. The transport devices have the result that the slivers are possibly somewhat stretched and slightly lengthened, in which case, however, because of the wave shape, different sliver lengths are furnished. When the drafting inside the drafting unit takes place with these different sliver lengths, unacceptably large draft deviations may occur in the drafting unit so that the yarn quality is negatively affected. This danger exists also when a (slight) preliminary draft occurs between the delivery roller pair and the feeding roller pair of the drafting unit. By means of the invention, it is provided that the slivers are slightly pretensioned between the delivery roller pair and the feeding roller pair of the drafting unit, without any resulting draft. As a result, the sliver lengths entering into the drafting unit are rendered uniform so that the drafting values can be maintained with high accuracy.
In an expedient further development of the invention, it is also provided that the distance between the delivery roller pairs and the pertaining feeding roller pairs of the drafting units is larger in the sliver travelling direction than the staple length of the spun fiber material. Preferably, the distance amounts to a multiple of the staple length. As a result, it is ensured that the pretensioning of the slivers takes place along a considerable length without any arising damage or undesirable drafts in the slivers.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.